The invention relates to a system and method for three-dimensional airway reconstruction, assessment and analysis. Specifically, the invention relates to a system and method for acquiring one- and two-dimensional data regarding a cavity, such as an esophagus or an airway, and manipulating that data to reconstruct a three-dimensional geometrical object representing that cavity. Suitable data collection methods include, but are not limited to, non-ionizing, non-invasive protocols including acoustic reflectometry, such as that performed by a DOS®- or Windows®-based pharyngometer or rhinometer. The resulting three-dimensional geometric object of the subject cavity can be used for diagnostics assessments, such as cavity constriction/obstruction, and therefore aid in the management and treatment of the constriction/obstruction, evaluate the efficacy of management and treatment of the constriction/obstruction and also provide information for use in outcome analysis, as well as forensic and medico-legal evaluations of diagnosis and treatment of cavity constriction/obstruction.
1. Field of the Invention
Obstruction/constriction of certain body cavities, such as airway passages, can create serious health problems. For example, sleep apnea is a debilitating and life-threatening condition that affects people worldwide. Sleep apnea occurs when tissues in the upper airway block the breathing passages. Obstructive sleep apnea is the most common type of sleep apnea. Normally, the muscles in the upper part of the throat allow air to flow into the lungs. When a person with obstructive sleep apnea falls asleep, these muscles are not able to keep the air passage open all the time. When the airway closes, breathing stops, oxygen levels fall and sleep is disrupted in order to open the airway. The disruption of sleep usually lasts only a few seconds. These brief arousals disrupt continuous sleep and prevent obstructive sleep apnea sufferers from reaching the deep stages of slumber, such as rapid eye movement (REM) sleep, which the body needs in order to rest and replenish its strength. Once breathing is restored, obstructive sleep apnea sufferers fall asleep only to repeat the cycle throughout the night.
Sleep apnea is suffered by adults and children alike. Sleep apnea can cause the sufferer to be sleepy throughout the day and is associated with cardiovascular disorders, including hypertension, coronary artery disease, heart failure, cardiac arrhythmia, stroke and metabolic abnormalities. Sleep apnea can be treated today by both surgical and non-surgical approaches. For example, by use of Continuous Positive Airflow Pressure (“CPAP”), the sufferer wears a mask that supplies a steady stream of air during sleep, where the airflow keeps the nasal passages open sufficiently to prevent airway collapse and apnea. Weight loss, change of sleep habits, behavior modification and wearing of oral appliances during sleep can also promote normal sleep.
In addition, people suffer from airway obstructions or constriction/narrowing (stenosis) due to congenital conditions and/or accidents.
In each case, evaluation of a cavity such as an airway is a valuable tool in analyzing a problem, and then developing a management and/or treatment plan for the sufferer of the problem. Also, evaluation of a cavity such as an airway is useful in providing information on outcome analysis for management and/or treatment plans for both care providers and insurance providers. Additionally, evaluation of the cavity has forensic and medico-legal uses.
2. Description of Related Art
Methods for acquiring data regarding the anatomy of body cavities and organs are known. For example, techniques such as radiographs (x-rays), including lateral cephalographs; CT scans, including cone-beam tomography, and nuclear MRI are often used to image body organs and cavities for evaluation and diagnostic purposes. These techniques have limited uses, however. Radiographs, including cephalographs, and CT scans expose the patient to potentially harmful ionizing radiation requiring appropriate precautions. Also, certain patient groups such as pregnant women might be excluded from such protocols. Also, certain techniques such as CT scans and nuclear MRI require post-processing of data to isolate certain cavities, such as the airway, because all tissues, including skin, muscle, bone, etc., are imaged simultaneously. Other techniques, such as cone-beam tomography, generate huge file sizes, which may exceed the resources available at a typical care-provider's office. Additionally, these techniques tend to be expensive, time-consuming and often require specially trained personnel.
Acoustic reflectometry is a non-invasive, non-ionizing protocol that produces a “one-dimensional” curve of the distance into the airway versus a two-dimensional cross-sectional area map of the upper airway. For example, U.S. Pat. No. 5,316,002, issued to Jackson et al. entitled “Nasopharyngealometric Apparatus and Method,” the disclosure of which is incorporated by reference, discloses an apparatus and method for: determining the profile of the nasopharyngeal cavity by introducing acoustic signals into the nasal cavities of a subject; detecting the acoustic signals and acoustic reflections; generating electrical signals proportional to the amplitude of the acoustic signals and acoustic reflections; determining the length of the nasal septum separating the nasal cavities, and computing the value of the area-distance function of the nasopharyngeal cavity from the electrical signals and the length of the nasal septum. U.S. Pat. No. 5,823,965, issued to Rasmussen entitled “Device for Reflectometric Examination and Measurement of Cavities,” the disclosure of which is incorporated by reference, also discloses an apparatus and method for reflectometric examination and measurement of human and animal cavities such as air and food passages. U.S. Pat. Nos. 5,746,699 and 5,666,960, both issued to Fredberg et al. and both entitled “Acoustic Imaging”, the disclosures of which are incorporated by reference, disclose an apparatus for providing an output signal characteristic of the morphology of the respiratory tract. A transducer launches acoustical energy toward the opening of the tract, producing an incident wave and a reflected wave to form a transient wave-field representative of the morphology of the tract. In each of these disclosures, the result is a “two-dimensional” measurement of the cross-sectional area of the measured cavity as a function of a “one-dimensional” distance into the cavity.
Practitioners have used acoustical reflectometry to assess preoperative and postoperative nasal septal surgery; see LARRY SHEMEN, M.D., F.R.C.S., F.A.C.S. and RICHARD HAMBURG, M.D., F.A.C.S., “PREOPERATIVE AND POSTOPERATIVE NASAL SEPTAL SURGERY ASSESSMENT WITH ACOUSTIC RHINOMETRY,” presented at the Annual Meeting of the American Academy of Otolaryngology-Head and Neck Surgery, Washington, D.C., September 29-Oct. 2, 1996, p. 338. The authors reported that the acoustic rhinometer allows objective measurement of nasal cavity volume, which is crucial in the diagnosis of nasal dysfunction. Such objective measurement allows for planning of appropriate treatment and evaluation of results after medical or surgical treatment. The authors also noted that objective documentation of nasal obstruction before and after surgery is being demanded by third-party payers, and allows for comparison of alternative procedures.
Other practitioners have noted that acoustic reflectometry can detect within seconds, and without the use of capnography, characteristic, distinctive and specific area-length profiles for both endotracheal and esophageal intubation. See DAVID T. RAPHEAL, M.D., Ph.D., “ACOUSTIC REFLECTOMETRY PROFILES OF ENDOTRACHEAL AND ESOPHAGEAL INTUBATION,” Anesthesiology. 92(5): 1293-1299, May 2000.
Certain practitioners have reported on the size and pressure/area relationship of the pharynx as important factors in the pathogenesis of obstructive sleep apnea. See BRIGADIER GENERAL IBRAHIM KAMAL, M.D., “NORMAL STANDARD CURVE FOR ACOUSTIC PHARYNGOMETRY,” available from the ENT Department, Police Authority Hospital, 26 Makram Oubaid Street, Nasr City, Egypt. Dr. Kamal reported that assessment of the upper airway for possible site(s) of obstruction/constriction is one of the keys to successful management of the condition, and that acoustic pharyngometry has the potential for localizing such sites. Dr. Kamal further reported that the acoustic pharyngometry technique is easy, rapid and cost-effective.
Acoustic reflectometry has also been used in connection with detection of conditions of the middle ear. For example, U.S. Pat. Nos. 5,868,682 and 5,699,809, both issued to Combs et al. and both entitled “Device and Process for Generating and Measuring the Shape of an Acoustic Reflectance Curve of an Ear”, the disclosures of which are incorporated by reference, disclose a device and process for analysis of acoustic reflectance of components of an ear. The results can assist in diagnosis of an ear pathology such as abnormal pressure, presence of fluid in the middle ear or conductive hearing loss.